Find n | C # program to find n - th number containing only 4 and 7. ; If n is odd , append 4 and move to parent ; If n is even , append 7 and move to parent ; Reverse res and return . ; Driver Code
using System ; class GFG { static string findNthNo ( int n ) { string res = " " ; while ( n >= 1 ) { if ( ( n & 1 ) == 1 ) { res = res + "4" ; n = ( n - 1 ) / 2 ; } else { res = res + "7" ; n = ( n - 2 ) / 2 ; } } char [ ] arr = res . ToCharArray ( ) ; Array . Reverse ( arr ) ; return new string ( arr ) ; } public static void Main ( ) { int n = 13 ; Console . Write ( findNthNo ( n ) ) ; } }